A2L chiller in a plant room: charge, ignition sources and signing off
A small hotel refurbishment has installed a 45 kg R-32 (A2L) air-cooled chiller in a newly built plant room measuring 5.0 m x 4.0 m x 2.8 m, with a louvred door and no mechanical ventilation. The room also houses the electrical distribution board, a gas-fired boiler with a permanent pilot light, and two spare gas cylinders left by the previous tenant. The contractor's commissioning sheet asks you to leak test the system and to 'sign the risk assessment' before the hotel opens. The practical limit used for R-32 in an occupied space is 0.30 kg/m3.
1. Calculate the room volume and the maximum unmitigated R-32 charge, and state what the result means for this installation.
Read the worked answer
Working
- Volume = 5.0 x 4.0 x 2.8 = 56 m3.
- Maximum unmitigated charge = 56 x 0.30 = 16.8 kg of R-32.
- Installed charge = 45 kg, i.e. 28.2 kg above the unmitigated limit, about 2.7 times it.
What it means
- This cannot be treated as a normal plant room. The design must include mitigation: a refrigerant detection system with alarm inside and outside the room, automatic emergency ventilation sized to keep concentration below the practical limit, restricted access and appropriate warning signage.
- R-32 is A2L (lower flammability), so ignition sources matter: the boiler pilot and the distribution board are exactly the kind of equipment that must be assessed, separated or relocated. Cylinders left in the room are a stored-charge and ignition/impact risk and should be removed.
Judgement point
- The F-gas leak-check thresholds do not answer this question – it is an EN 378 / manufacturer design issue. Your calculation proves the as-built arrangement is not adequate, and that is a reportable finding, not something to paper over at commissioning.
2. You are asked to pressurise and charge the system in this room. Set out the safety controls and PPE you would insist on before starting.
Read the worked answer
Before work
- Confirm the mitigation is installed and working (detector calibrated, ventilation proven) or that the charge is being added with the boiler isolated and the room ventilated and controlled.
- Method statement and risk assessment for A2L work; permit to work if the hotel is live; exclusion zone and signage.
- Gas detector suitable for R-32 in use, plus a fire extinguisher appropriate to electrical and gas fires.
Ignition control
- No smoking, no naked flame, no hot work without a permit and gas-free confirmation; bond and earth equipment; avoid static-generating clothing and plastic sheeting; use intrinsically safe or A2L-rated tools where required.
Cylinder handling
- Cylinders upright and secured on a trolley, valve cap on when moved, never dropped or rolled; keep below the maximum storage temperature and out of the plant room once the task is done.
PPE
- Safety glasses or goggles, low-temperature gloves for liquid contact and frostbite protection, safety footwear, and hearing protection if the plant runs. R-32 has low toxicity but is an asphyxiant in a confined space, so ventilation is a control, not an option.
3. The contractor hands you a leak detector they have bought and asks you to fit it and sign the risk assessment as complete. How do you respond?
Read the worked answer
Fitting the detector
- A detector is only a control if it is fit for purpose: correct refrigerant, correct range, positioned where R-32 will collect (it is heavier than air, so low level and near the likely leak points), alarm repeated outside the room, and installed to the relevant product and system standards.
- It must be capable of being tested and calibrated, and the annual inspection must be recorded – that inspection is what allows the statutory leak-check frequency to be halved.
Signing the risk assessment
- Do not sign a design risk assessment you did not write and cannot verify. The assessment covers room mitigation, charge limits, ignition sources, ventilation performance and emergency procedures; that needs the designer and the manufacturer's data.
- Sign only the parts within your competence and certification – the tightness test, charging, records and the as-left condition – and record clearly what you could not verify and why.
Judgement point
- Pressure to 'just sign it' before opening is exactly when a written, dated note to the client protects both the occupants and you.